The invention relates to a method for operating an open-end rotor yarn spinning unit, and an apparatus for carrying out the method.
Different types of open-end rotor spinning units are known, which comprise a spinning rotor that rotates during the spinning process at a high rotational speed in a rotor housing which is closed by a cover element and kept under a vacuum. The open-end rotor spinning units differ both with respect to the bearing mount of their spinning rotors and with respect to their drive.
The majority of the open-end spinning rotor units that are currently on the market and disclosed, for example, in DE 103 05 279 A1, and corresponding U.S. Publ. No. 2004/154280 comprise spinning rotors that are supported with their rotor shaft in the cusp of a so-called twin disk bearing. In the case of such twin disk bearings, it is common to provide for axially securing the spinning rotor, an additional thrust bearing, which may be constructed either as a mechanical bearing or as a magnetic bearing. The drive of such bearing mounted spinning rotors normally occurs via a tangential belt which runs the length of the machine, with a contact roll causing the tangential belt to lie against each rotor shaft of the spinning rotor. The above described bearing and drive assemblies permit spinning rotor speeds greater than 100,000 rpm.
Besides these spinning rotors that are mechanically supported in twin disk bearing assemblies, it is also known to support spinning rotors in bearing assemblies in a noncontacting manner, and to operate them by individual electric motors, for example, by electromagnetic drives. Noncontacting, smoothly operating bearing assemblies are, for example, air bearings or magnetic bearings.
DE 100 22 736 A1 and corresponding U.S. Publ. No. 2002/002816 describe an open-end spinning unit with such a magnetic bearing assembly. In this assembly, the rotor shaft of the spinning rotor is supported in a noncontacting manner via two bearing points that are arranged in axially spaced relationship and formed by paired permanent magnets. These paired permanent magnets are constructed and arranged such that respectively opposite magnet poles face each other, so that respectively repulsive magnetic bearing forces are operative between the permanent magnet on the rotor side and the permanent magnet on the stator side.
The permanent magnets on the stator side are also surrounded by electric windings that can be switched in a defined manner, and which permit increasing or decreasing the magnetic forces as a function of the direction of the electric current flow. In this process, the electric windings are activated via a corresponding control device as a function of signals of a sensor, which measures the axial deviation of the rotor from its desired position.
The drive of such spinning rotors that are supported in a noncontacting manner, normally occurs by means of individual electric motor drives, preferably DC motors, which are each arranged between the magnetic bearing points.
Irrespective of the type of bearing mount and/or the type of the drive of spinning rotors, it is necessary to open such open-end spinning devices from time to time, for example, for cleaning the spinning rotor. This means that the particular spinning rotors must first be slowed down to a standstill. After opening the rotor housing, they can then be cleaned, for example, by a mechanical scraper of an automatically operating piecer carriage or by the operating personnel.
Because of the high rotational speeds, at which the spinning rotors rotate during the spinning process, one must make sure that the piecer carriage or the operating personnel can open the rotor housing only when the spinning rotor has slowed down to no more than a considerably reduced speed. Furthermore, when restarting the spinning rotor, it must be made sure that the rotor housing is properly closed by a cover element.
For this reason, open-end rotor spinning units with a spinning rotor that is mechanically supported in a twin disk bearing assembly and adapted for being driven by a tangential belt, comprise a rotor brake, whose brake shoes engage the rotor shaft in the fashion of tongs and, in so doing, decelerate it. This means that the rotor brake starts acting, as soon as the cover element that closes the rotor housing is actuated in the direction of “opening”.
At the same time as the rotor brake is actuated, a contact roll which brings during the spinning operation the tangential belt of machine length into frictional contact with the rotor shaft of the particular spinning rotor, is raised and thus separates the driving engagement of the rotor shaft and the tangential belt.
The above described rotor brake remains in contact with the rotor shaft, until the cover element engages again in the prescribed manner, i.e., the rotor housing is properly closed.
In practical operation, the above described devices have proved themselves in connection with spinning rotors that are supported in twin disk bearing assemblies. In the case of spinning rotors that are driven by individual motors, in particular when these spinning rotors are supported in a magnetic bearing assembly, such devices are however less advantageous or unusable for various reasons.
Spinning rotors that are driven by individual motors are normally not decelerated to a standstill, for example, by a mechanical rotor brake, but electrically. This means that in the case of such drives the flow direction of the motor current is simply reversed for stopping the spinning rotors. Such a braking current permits decelerating spinning rotors that are driven by individual motors, to a standstill within the shortest time and in a material protective manner. However, these individually driven and magnetically supported spinning rotors require taking additional measures which ensure that before opening the rotor housing, the spinning rotor rotates only below a predetermined rotational speed limit, and in particular that the rotor housing is also properly closed before a restart of the spinning rotor.
The known open-end spinning units with spinning rotors that are driven by individual motors and supported in magnetic bearings, are therefore equipped with special sensor devices, which monitor the proper closing of the rotor housing.
Based on the above-described state of the art, it is an object of the invention to develop a method and an apparatus, which enable a cost favorable and reliable operation of open-end rotor spinning units, whose spinning rotors are driven by individual motors and supported in magnetic bearing assemblies.